/***
 * number 数字
 * + 正数、负数、零、小数...
 * + NaN： not a number
 */

console.log(typeof NaN);
console.log(typeof Infinity);
console.log(typeof -Infinity);

console.log(NaN == NaN);
console.log(isNaN(NaN));
console.log(Object.is(NaN, NaN));